The present invention relates to a light scanning device.
Light scanning devices are known as a device for writing and reading information by scanning a light beam. In one type of such a light scanning device, a light beam emitted from a light source is focused as a linear image, and a rotating polygon mirror has a reflecting surface positioned near the linearly focused image for deflecting the light beam at a constant angular velocity. The deflected light beam is focused as a beam spot on a surface by a focusing lens system for scanning the surface.
Such light scanning devices suffer from various problems such as noise of the rotating polygon, dirt on the rotating polygon, leakage of lubricating oil from the rotating polygon to focusing optical systems, and deposit of leaked lubricating oil on the focusing optical systems. In order to circumvent these drawbacks, there has been proposed a light scanning device including a housing which sealingly accommodates a rotating polygon and has a window in which a transparent plane-parallel plate is fitted (see Japanese Laid-Open Utility Model Publication No. 59-123821). A light beam emitted from a light source is applied to the rotating polygon through the plane-parallel plate, and the light beam deflected by the rotating polygon is then applied to a focusing lens system. However, the proposed light scanning device has not been designed to eliminate a ghost produced by a reflection from the transparent plane-parallel plate and an effect of the astigmatic difference of the plane-parallel plate on the focusing performance of the focusing lens systems.